Extensive regions of the world, particularly the nations denominated the Third World, lie in the path of the trade winds and are surrounded by seawater. Many of these regions lack a source of potable water and could be rendered arable and productive if irrigation water could be made available. Particular regions of note include the Horn of Africa, the Caribbean Islands and large coastal areas of Australia.
The desalination of seawater has hitherto largely depended on fossil fuels as the power source. The rising cost and increasing scarcity of fossil fuels render them substantially unavailable to poorer countries of the world. Yet the steady increase in the world population puts increasing strain on the water supplies and critically increases the need for a practical and cost effective means to desalinate seawater.
Desalination of seawater by water wave-powered reverse osmosis has not received serious attention in the past, possibly because efficient and cost effective means for providing seawater at the required pressure was not known. However, some attention has been given generally to the efficient extraction of power from waves. For example, Count in Proceedings of the Royal Society, London A, 363 559-573 (1978); IEEE Spectrum 42-49 Sept. (1979) and Evans in Journal of Fluid Mechanics 77 Part 1, 1-25 (1976) showed that the efficiency of a wave energy extraction device comprising a mooring means and a wave follower depends on the so-called natural period of the device and the power-extraction damping of the motion of the wave follower.
The natural period of the device, as the term is here used, pertains to the natural period of oscillation of the follower which, for maximum efficiency ought to match the period of the waves when in use. Among controllable variables, the natural period depends primarily on the mass of the wave follower which is kept low so as to minimize inertia. A follower is most efficient when it is non-Archimedean, i.e. is pulled underwater at least in part thus displacing somewhat more water than its own weight.
The extraction of power from the movement of the wave follower with respect to its mooring naturally causes damping which affects the efficiency of the device. The extraction of power in such a way as to maximize the power yield is an important object of this invention.
As is apparent, too much damping or constraint on the movement of the wave follower can result in no movement at all and thus no extraction of power; the classical physicist would say that although force is provided, the force does not act through a distance and hence no work is done. At the other extreme, it is apparent from similar logic, that if no constraint is applied, no power is extracted. Maximum power is extracted somewhere between these extremes.